Federal and state governments, along with vehicle manufacturers, test and certify new vehicle emissions, and also carry out some in-use testing of older vehicles. These tests comply with the Federal Test Procedure (FTP) as outlined in the Federal Register, which is a carefully designed and specified three-phase test under "cold transient," "cold stabilized," and "hot transient" conditions. The vehicle is generally driven in a series of accelerations, decelerations, stops, and starts on a chassis dynamometer, whose inertia and friction are specifically set for each vehicle. The emissions from each phase are collected at a constant volume into a sample bag, and the concentrations of each species of pollutant are determined from the integration of the entire bag, with a final result given in grams of pollutant per mile.
The driving course is modeled after a "typical" summertime commute to work in Los Angeles. Each of these tests takes at least twelve hours to complete and costs in excess of about $700, in 1990 dollars. The reproducibility of the results for a given vehicle is believed to be plus or minus 20%, controlled mainly by the repeatability of the vehicle emissions system and not by the test system or gas analysis protocols. Presently available computer models are based on the concept that the FTP emissions measured from a fleet of vehicles are well correlated, although not necessarily one to one, with the emissions that the same fleet would exhibit under in-use driving conditions. However, since very little is known about actual on-the-road fleet emissions, it is impossible to truly gauge the accuracy of this assumption.
In addition to any new car emission certification programs, there are also state inspection and maintenance (IM) programs designed to test every vehicle in a given area that are, therefore, much less rigorous tests. Most sophisticated centralized IM testing programs use a very much shorter FTP-type test on a chassis dynamometer, or one or two fixed loads and speeds, and measure the steady-state emissions as a percentage of the exhaust. Many centralized, and all current decentralized programs measure only idle emissions as a percentage of the exhaust at one, or possibly two, engine speeds.
In late 1986, a fuel efficient automobile test (FEAT) system was developed and designed to remotely detect carbon monoxide and carbon dioxide levels in vehicular emissions and to make specific measurements on individual vehicles. This system is more specifically described in an article entitled "Automobile Carbon Monoxide Emission," Environmental Science Technology, vol. 23, pages 147-149, 1989. Also see "IR Long-Path Photometry: A Remote Sensing Tool for Automobile Emissions," Analytical Chem., vol. 61, pages 671A-676A, 1989. This particular device, while extremely accurate, had its limitations in that it was unable to identify the specific vehicles found to be emitting carbon monoxide in excess of acceptable levels so that the vehicle owner could be subsequently contacted and advised to adjust or repair or modify the vehicle to control its emissions. Moreover, while it was capable of measuring carbon monoxide and carbon dioxide, it was not capable of measuring other emission components or the temperature at which the vehicle was operating, the knowledge of which would be extremely valuable to have.
As indicated, it is known to the inventors that the basic idea of remotely measuring vehicle emissions is not a new one. Lockheed Missiles and Space Corporation first attempted construction of an across-the-road monitor, the successful operation of which was never published. L. Chaney, "The Remote Measurement of Traffic Generated Carbon Monoxide," J. Air Pollution Control Association (vol. 33, pages 220-222, 1983) proved that carbon monoxide fumes (and only carbon monoxide) from passing vehicles could be observed in real-time with a gas filter correlation radiometer. However, Chaney's system did not include any of the parameters required to accurately measure emissions data from vehicle exhaust plume observations.
It is also well known that vehicle exhaust emissions change as a function of the operating temperature of the vehicle engine and exhaust system. When a vehicle is first started, its engine and exhaust system are often in a relatively cold state that leads to incomplete combustion in the engine cylinders and less than optimal performance of the catalytic converter and other components of the exhaust system in controlling pollutants in the exhaust. As the engine and exhaust system gradually warm during operation, the chemical composition of the vehicle exhaust will gradually shift to values that more accurately reflect steady-state operation of the vehicle. Emissions data from cold vehicles are inherently high and therefore tend to be an unreliable indicator of the vehicle's overall emissions levels. Relatively high levels of emissions from a cold vehicle may falsely identify the vehicle as a gross polluter, when in fact, the vehicle's emissions levels are within acceptable limits after the vehicle has warmed up to its normal operating condition. This problem has been identified in other systems for measuring and controlling vehicle emissions, as follows:
______________________________________ Inventor U.S. Pat. No. Issue Date ______________________________________ Jowett et al. 3,958,122 May 18, 1976 Jowett et al. 3,973,848 Aug. 10, 1976 Fastaia et al. 4,160,373 July 10, 1979 Kreft 4,348,732 Sept. 7, 1982 Ogita 4,432,316 Feb. 21, 1984 Wolfrum et al. 5,002,391 Mar. 26, 1991 Maus et al. 5,255,511 Oct. 26, 1993 Maus et al. 5,307,626 May 3, 1994 ______________________________________
Jowett et al. disclose an exhaust gas analyzer having pressure and temperature compensation. The exhaust gas emissions are fed into a sample cell 28 having a thermister 40 to measure the temperature the exhaust gas. This system is apparently intended to measure exhaust emissions from a stationary vehicle and would not be suitable for measuring emissions from a series of moving vehicle on a roadway under actual driving conditions.
Fastaia et al. and Kreft disclose other examples of exhaust gas analyzers for measuring emissions from a stationary vehicle. Again, a thermistor is employed to measure the temperature of the exhaust gas passing through a sample cell.
Ogita discloses an apparatus for controlling hydrocarbon emissions from automobiles equipped with a catalytic converter while the engine is cold.
Wolfrum et al. disclose a gas analysis system for flue gases exhausted from power plants and industrial facilities. A temperature detector 37, such as a radiation pyrometer, is used to measure the temperature of the flue gases.
Maus et al. disclose a system for operational monitoring of a catalytic converter of the exhaust system of an engine. The temperature of the walls of the catalytic convertor is measured for at least two regions within the catalytic converter. This information is used to control operation of the engine.
None of the prior art systems are capable of remotely measuring the temperature of moving vehicles on a roadway under actual operating driving conditions. Therefore, a need exists for a system to remotely determine vehicle temperature in order to validate or invalidate emission measurements for each vehicle.